During open heart surgery and in some emergency cardiac or cardiopulmonary situations, it is necessary to have some means for pumping the blood either alone or in conjunction with an oxygenator to replace or support the patient's cardiac or cardiopulmonary functions.
Prior art extracorporeal device technology has used individual devices for the functions of pumping blood and oxygenating blood. Historically, the roller pump has been the blood pump of choice for extracorporeal circulation, mainly due to its reasonably low levels of blood damage and priming volume. However, because it is a positive displacement pump, high, unsafe pressures can develop if the discharge line is inadvertently closed off or restricted. Furthermore, the drive mechanism and motor is relatively cumbersome, making it less than ideal in terms of ease of use.
Recently, the centrifugal pump has come into some favor, primarily because it is safer and easier to use. It is safer because it is not a positive displacement pump, and it is easier to use because its drive mechanism and motor cam be made compact and relatively mobile. Early centrifugal blood pumps had vaneless impellers, and momentum was transferred via viscous drag between the impeller surfaces and the blood. Although these had the potential to decrease blood damage, relatively large surface area was required, requiring a large priming volume.
More recently, centrifugal blood pumps with vaned impellers have been introduced in order to reduce priming volume. A recent example of such a pump is disclosed in U.S. Pat. No. 5,017,103, to Dahl. Although blood damage, as measured by red cell hemolysis, can be reduced to acceptable levels with pumps of this type, there is still some increase due to the turbulence created by the vanes. A further disadvantage results from the backflow, radially inward, which occurs in the fluid spaces between the vanes, thus decreasing the potential delivery pressure of the pump. Additionally, the overall inlet and channel volume of this pump is still large relative the impeller envelope volume. Thus, priming volume is still relatively high.
U.S. Pat. No. 4,253,798, to Sugiura, discloses a centrifugal pump which is not disclosed for use as a blood pump. The pump has an impeller comprising a main disc and a plurality of vanes which project axially from at least one side of the disc. A fluid passage is formed between each pair of adjacent vanes having a cross section that decreases as the flow passage projects radially outward. The reduced passage width is intended to decrease the fluid vortices in the passage to improve pump delivery at low flow rates. In order to create the radially decreasing passageway, it is necessary to have a large interior impeller diameter. Furthermore, since the pump has two flow inlets, the total inlet and passageway volume of this pump is large compared to the total impeller envelope volume. If the Sugiura pump is used to pump blood, it will require an excessively large priming volume. The pump also has ribs placed at the midpoint of the passageways to provide mechanical integrity. These ribs increase the potential for fluid spillage, increasing fluid turbulence and decreasing pump efficiency. This would create serious problems for pumping blood, due to the increased likelihood of blood damage.
Prior art blood pumps which are used in conjunction with an oxygenator are typically connected together in an extracorporeal tubing loop to receive venous blood from the patient and return arterial blood back to the patient. One of the problems with these types of devices, such as that shown in U.S. Pat. No. 3,183,908, has been that large amounts of blood are required to prime the oxygenator, the pump, and the tubing between the oxygenator and the pump.
Some attempts have been made to incorporate the pumping and oxygenation functions in a single device. For example, U.S. Pat. No. 3,841,837 discloses a blood oxygenator or dialyzer that achieves enhanced transfer through rotation of a cylindrically mounted membrane placed eccentrically inside a stator housing. Blood flows in the annular space between the rotor and the stator. Rotation causes a pumping action, thus causing pumping and oxygenation to occur simultaneously. All of these prior art devices have required relatively large amounts of fluid to prime the pump and oxygenator. There have also been difficulties with the safety and ease of use by the perfusionist. Furthermore, these devices can be quite costly to manufacture.
What is needed is a low priming blood pump which is safe, easy to use, and which causes minimal blood damage. What is further needed is a blood pump which can be readily integrated into a blood oxygenator housing. Such an invention is disclosed and claimed herein.